The safety cell in the BB2 is made of 1/2" aluminum honeycomb with 6 layers of carbon fiber, 3 per side. Hardpoints are incorporated to facilitate mounting the cell to the chassis as well as attaching belts, controls, etc. It is easiest to design these hardpoints in from the start. Not that they can't be added later, it's just much easier to build them in.
Overall we are extremely pleased with the cell. It is strong, light, and adds an extra dimension of safety for the driver.